The present invention relates to an optocoupler of the type having at least one light-emitting diode (LED) and one single photodiode chain optically coupled to the LED, and it, more particularly relates to this type of optocoupler wherein two FETs are connected in series each having a first and second connection, whose gate terminals and first terminals are connected to each other, and the first connection of the photodiode chain being connected to the gate connections.
Such a type of optocoupler has been described, for example, in the European Patent Application No. 48146. The energy for driving the FETs is solely derived from the photodiode chain. Upon illumination across a LED the photodiode chain generates a voltage, which drives the first of the mentioned FETs conducting. The second FET is blocked upon illumination of the photodiode chain. A load current then flows through the first FET and the integrated diode of the second FET. When the illumination stops the second FET becomes conducting and the first FET is blocked (non-conducting). The load current then flows through the second FET and through the integrated diode of the first FET.
The current supplied by the photodiode chain, in general, amounts to only a few microamperes. This means that the first FET can only be switched on rather slowly.